How RNAi Drugs Work—Silencing Genes to Treat Disease

A Natural Defense Turned Into Medicine

Every cell in the human body has a built-in system for shutting down unwanted genes. Scientists call it RNA interference (RNAi)—a process in which small RNA molecules intercept and destroy the genetic messages that tell cells to build specific proteins. For billions of years, organisms from plants to worms have used this mechanism to fend off viruses and regulate their own genes. Now, pharmaceutical companies have learned to harness it, creating an entirely new class of drugs that silence disease at its genetic source.

How RNA Interference Works

The central idea is elegantly simple. DNA stores the body's genetic blueprint, but to make a protein, a cell first copies the relevant gene into a molecule called messenger RNA (mRNA). That mRNA travels to the cell's protein-building machinery, where its instructions are read and executed. RNAi drugs intercept this process by introducing a synthetic small interfering RNA (siRNA)—a short, double-stranded RNA molecule designed to match a specific mRNA sequence.

Once inside a cell, the siRNA is loaded into a protein complex called RISC (RNA-Induced Silencing Complex). RISC unwinds the double strand, discards one half, and uses the remaining "guide strand" to hunt for its complementary mRNA target. When it finds a match, RISC cleaves the mRNA, destroying the message before the cell can build the disease-causing protein. A single RISC complex can destroy hundreds of mRNA copies, which explains why these drugs can last for months on a single dose.

The Delivery Problem—and How Scientists Solved It

For years after Andrew Fire and Craig Mello won the 2006 Nobel Prize for discovering RNAi, turning the science into medicine seemed impossible. Naked siRNA molecules are fragile—enzymes in the bloodstream shred them within minutes, and they cannot cross cell membranes on their own.

Two delivery technologies cracked the problem. The first approved RNAi drug, patisiran (2018), wraps its siRNA payload inside lipid nanoparticles (LNPs)—tiny fat bubbles that fuse with liver cells and release their cargo inside. The second and now dominant approach uses GalNAc conjugates: the siRNA is chemically attached to a sugar molecule called N-acetylgalactosamine, which binds to receptors found almost exclusively on liver cells. GalNAc-conjugated drugs are simpler to manufacture, can be injected subcutaneously, and are generally better tolerated than LNP formulations.

Seven Drugs and Counting

As of early 2026, seven siRNA drugs have received FDA approval, treating conditions that range from rare genetic disorders to common cardiovascular disease:

• Patisiran and vutrisiran — hereditary transthyretin amyloidosis
• Givosiran — acute hepatic porphyria
• Lumasiran and nedosiran — primary hyperoxaluria
• Inclisiran — high LDL cholesterol (administered just twice a year)
• Fitusiran — hemophilia A and B (approved 2025)

Inclisiran stands out for its reach: it targets a common condition—high cholesterol—and reduces LDL levels by roughly 50% with two injections per year, potentially replacing daily statin pills for millions of patients.

Beyond the Liver

Nearly all approved RNAi drugs target the liver, because GalNAc delivery is so efficient at reaching hepatocytes. The next frontier is delivering siRNA to other organs. Researchers are developing conjugates and nanoparticles that can reach the brain, lungs, kidneys, and tumors. In cancer, siRNA could silence genes that help tumors evade the immune system or resist chemotherapy—targets that traditional small-molecule drugs often cannot reach.

Experimental RNAi drugs are also entering trials for hypertension. Zilebesiran, an investigational siRNA that silences the gene for angiotensinogen—a key driver of blood pressure—has shown sustained blood pressure reductions lasting six months from a single injection in clinical trials published in the New England Journal of Medicine.

Why It Matters

RNAi drugs represent a fundamental shift in how medicine treats disease. Rather than blocking a harmful protein after it has been made—the approach of most conventional drugs—siRNA stops the protein from being produced in the first place. The result is therapies that are highly specific, long-lasting, and potentially applicable to thousands of diseases driven by known genetic targets. With over 85% of disease-relevant genes considered "undruggable" by traditional pharmaceuticals, RNA interference opens a vast new landscape for treatment.